Zinc base die-casting alloy



Patented Apr, 5, 1932 UNITED STATES PATENT OFFICE WILLIS M. PEIBCE AND EDMUND A. ANDERSON, O]: PALMEBTON, PENNSYLVANIA, I ASSIGNOBS TO THE NEW JERSEY ZINC COMPANY, OF NEW YORK, N. Y., A CORPORA- TIUN OF NEW JERSEY lblo Drawing.

This invention relates to zinc base-die-casting alloys and has for its object the provision of an improved alloy of this character.

The mechanical requirements of the die- ,a casting operation necessitate the construction of the melting pot and die from iron and steel. These metals are subject to attack by molten zinc and it has been found from experience that at least 0.25% aluminum must ltl he added to the zinc in order to minimize this attack sufficiently to secure reasonable life t'rom the apparatus. Alloys for die-casting must possess a suflicient degree of fluidity to properly flow into and completely fill the dies it used, and 2% or more aluminum appears to he necessary to secure'an adequate degree of tluidity. It has also long been known that aluminum increases the tensile strength of zinc and this, in itself, makes its presence in as zinc base die-casting alloys desirable in quantitles of from 2% to as much as 10 to 15%.

dine-aluminum alloys containing less than about 80% of aluminum undergo a structural change subsequent to solidification which is commonly known as a phase change or more specifically in this case as a eutectoid reaction. This phase change consists in the formation oll two crystalline forms or phases from one phase previously existing, and is accompanied P by certain changes in physical properties of the alloy, such, for example, as increase in density, hardness and tensile strength and decrease in ductility and impact strength.

This phase change may occur during the cooling of the alloy after casting or may through certain influences be retarded or inhibited. lln such cases it may take place gradually over a period of months at orditU nary temperatures.

A secondary stage of phase change which sometimes occurs is the growth or coalescence ot the extremely small particles of the new phases as first formed into larger particles.

This stage ma be accompanied by softening zmc BASE nrn-casrme ALLOY Application filed August 29, 1980. Serial No. 478,796.

or lowering of tensile strength and by an increase in ductility and impact strength.

Zinc-aluminum alloys in this range of composition are also subject to a type of disintegration commonly .known as intercrystalline oxidation. In extreme cases, under the influence of warmth and moisture, intercrystaL line oxidation may completely penetrate specimens of these alloys and cause swelling, warping and even complete disintegration. Intercrystalline oxidation is in some Way associated with and partly dependent upon the phase change.

It has heretofore been recognized that certain other metals when present in these zincaluminum alloys exercise important effects on either the phase change or the intercrystalline oxidation or both. For example, copper and magnesium are known to exert an in fluence on the phase change either in respect to the rate at which it takes place or the completeness of the reaction or in some other respect not fully understood. The particular effect produced by copper and magnesium on the phase change reacts favorabl in increasing the resistance of the alloys to intercrystalline oxidation. Lead, while not exerting any marked influence on the phase change, very seriously diminishes the resistance of these zinc-aluminum alloys to intercrystalline oxidation. Cadmium, though having a certain effect on the phase change, in the presence of lead usually diminishes the resistance of these alloys to intercrystalline oxidation.

Zinc base alloys suitable for die-casting are known and in use. An alloy containing 4% aluminum, 3% copper and the balance high grade zinc metal has been widely used and is satisfactory for many purposes. This alloy is, however, open to two objections. First, upon ageing, either at normal temperatures or at slightly elevated temperatures, the alloy suffers a serious loss in impact strength and a change in linear dimensions. Second, in the presence of moisture, and particularly in the t In ghe coukrse 051 an exhaustive investigacomposmn 1011 o zinc ase 'e-cast' allo s we have f 1)1und thatdthe tendency ifi zin -siluminum AHOY Alloy a oys to un ergo intercrystalline oxidation is g, a greatly diminished by the elimination of ggggg -ee harmful impurities notably lead and tin and yo i m man We i 3521 under certain conditions cadmium. This was taken advantage of in the preferred composi- Properties as cast tion of the alloy described in the United States patent of Peirce and Anderson No. 0 strength. flat 41.3 44. 1,596,761, dated August 17, 1926 by the use 133$?3$t:f?fi:::::: "'i "123 0 of high grade zinc metal (e. g. Horsehead bragd) as the Zing:1 base of the alloy. Higl]: Properties after ten days in steam at 95 0'.

a e zinc meta owever contains as muc as 0.05% of lead and to prdduce an allo sufi ns fla 9,600 32,900. ficiently free from intercrystalline oxi ation ini'tttiitfifit tififif? la'aog i with this amount of lead present additions g ggigg 2'31: gggg of bothhcopper arid maignegium are necessary f since t ese meta s in ivi ually tend to retard or prevent intercrystalline oxidation and ?i g fgxfi ifg g g iig igitg 2 ri g z ggifggz ggfi gig g more or less linens. The impact strength is indicated in Continued experiments with zinc metal gg gfi f igz sg gi gigg' i i s: 2:: containing materially less lead than present tions 3/ in and 1/ in width h high grade zinc metal indicabtfld definitgly We g 2 t att ere were im ortant ossi ities int is direction. We ha e now discovered that if g 'n g gf f gg z gg 22 2;??? 5; 2:22;

fitiefi iifiiifg tgiti ms s bilwcehzimrl zinc base alloy) is less than 0.02% with tin fi g g fif fi i ess t an 001% o substantially absent, the presence of copper 2 A zinc base consistin of s in excess of 2% but not exceeding about 6% alm'hinum about 37y) er i the g (and without magnesium very materially zinc metal of hi h lirit rith at least 93 3 8 I tards intercrystalh'ne oxidation, and thatsuch 'zinc V g p y 0 gg i ggg gi z field .*P as a l3. zinc base alloy composed of 2 to 5% 10 Our present invention accordingly contemi g gs g fi zf fiig z a 5 11:1 :8: Plates zinc base die'casting Substan' zinc base is zinc metal of hi h urit co 7 tilagly free of naginlesium and containing from mining at least 99 98% zinc g P y a ut 2 to10 0 uminum, cop er in excess of and not exceeding 5 in which wins testimony whereof we afiix our s1gna-. the zinc base is zinc metal of high purity T WILLIS M PEIRCE containing at least 99.98% zinc and prefer- EDMUND ANDERSON ably containing 99.99+ zinc. Our present preferred composition of the alloy of the invention is about 4% aluminum, about 3% 11! copper and the balance zinc metal of high nrity containing -99.99+% zinc. The zinc nptal of high purity should contain notmore than about 0.01% lead plus cadmium. Ve I satisfactory results have been secured wit zinc metal containing 99.99+% zinc, less than- 0.003% lead, less than 0.003% cadmium and less than 0.001% tin. Tin should be substantially excluded from the alloy and in no case should the tin content exceed about 0.001%.

The following table illustrates the important physical properties of a die-castin made of an alloy of the invention. Alloy 0.1 is of the composition heretofore largely used presence of warmth and moisture together, the alloy undergoes intercrystalline oxidat1on whlch causes serious changes in physical properties and dimensions.

as a zinc base die-casting alloy made up of Alloy N0. 2 is an 

